Need to stop OpenStack allocating neutron ports from the "VIP range"

[lathiat]

This is required by both stsstack-bundles and the charmed test runner

A couple of possible solutions

1. Allocate intentionally un-used undercloud neutron ports with the VIPs we plan to use - watch out for accidentally cleaning them up
2. Modify the neutron subnet allocation_range to remove these IPs. I tried to do this in terraform, the problem is the subnet range is dynamically allocated by OpenStack during the subnet creation, so terraform cannot calculate the allocation_range because its a circular dependency. We can however still manually modify this ourselves, and terraform probably won't roll it back, because it's not tracking the value.